1. Field of the Invention
The present invention relates to the field of power inverters used for electronic lighting ballast and the ability of the ballast to supply line isolated power to be used by various ballast accessories mounted external to said ballast. The isolation allows connection of devices external to the fixture in which the ballast is mounted while complying with Underwriters Laboratories Standards. The isolation is also applied to circuitry internal to the ballast to allow the ballast to be connected to a low voltage hard wired control system while meeting Underwriter's Laboratories (UL) requirements for the electrical separation of control voltage and power line voltage. A unique method of applying power at start up is also disclosed.
2. Brief Description of the Prior Art
There are many varied public domain circuits involving the generation of high frequency inputs for driving fluorescent lamps, compact fluorescent lamps, high intensity discharge and other forms of gas discharged lighting. There are a number of gas discharge lighting applications where it is desirable to adjust the amount of light generated based upon the time of day, the particular application being illuminated, energy reduction requirements based on momentary energy demand and/or user preferences. This, is often referred to, as dimming. Such a device was disclosed in my U.S. Pat. No. 4,277,728, now expired. In most cases some sort of external control system is required to tell the ballast how much light, the device it is ballasting, should be emitting based in on the some form on feedback as to how much light is measured in the illuminated area. In other cases elaborate central control systems are employed that send information to each ballast via control wire, power line carrier (PLC) or a wireless system.
Some or all of these systems require some sort of receiving or decoding device to interpret the signal and tell the ballast what to do. Systems of this sort that are normally mounted outside the ballast enclosure and must have power from some source to operate. If connections to these devices extend outside the fixture in which the ballast is mounted and are connected to some sort of low voltage wiring system or external devices that can be accessed buy unqualified personnel they must be electrically isolated from the normal AC line power. In these cases the logic power used within the ballast cannot be brought outside the ballast to power these devices. In the market place today some sort of additional power supply is provided at extra cost or, in the case of low voltage wiring systems, a separate wire or wires are provided to bring operational power to these external devices.